Syrian rebels knocked down army defenses and moved in on the country's second largest airport Wednesday, reportedly killing more than 40 soldiers and bringing them closer to what could be their biggest conquest since the beginning of the civil war.

Control of Aleppo International Airport and a military air base next to it would be a huge strategic shift for Syria's northeastern region, giving the opposition a potential air hub enabling aid and other flights.

Still, activists said it could be days before the rebels would be able to push their way into the airport, 4 miles from the contested city center, and even then, it was unclear whether they would be able to retain control of the sprawling facility for long.

The country's airspace is firmly controlled by the government, which uses its warplanes to indiscriminately bomb rebel strongholds.

The advance on the airport, which stopped handling any flights weeks ago because of the fighting, follows other strategic gains. Rebels this week captured the nation's largest dam and a military base near Aleppo. They have also brought the fight closer to Damascus, seat of President Bashar Assad's government, moving to within a few miles from the heart of the city.

The government tried to reverse the gains with a series of air strikes in several locations across the country Wednesday. In Jobar, a rebel stronghold in northeastern Damascus, 13 people were killed in government shelling, according to the Syrian Observatory for Human Rights, in Britain. Fighter jets also carried out air strikes on rebel positions in the central province of Homs, it said.

The rebels have been pushing their way into the capital since last week. The foray marks the opposition's second significant attempt to storm Damascus since July, when the rebels captured several neighborhoods before being swept out by a swift government counteroffensive.

Since then, the regime has buckled down in Damascus, setting up checkpoints and controlling movement in and out of the city. The heavily defended city so far has been spared the kind of violence that has devastated whole neighborhoods in other major cities such as Aleppo.

The rebels have had the most success in northern Syria, and have captured large parts of Aleppo, Idlib and Raqqa provinces since the conflict began in March 2011.